Why do different bacteria exhibit different chemotactic responses? One possible reason is that different bacteria have evolved for different environments. For example, while E. coli might be expected to inhabit a resource-rich environment, marine bacteria experience a harsh environment in which attractant is localized in short-lasting patches [1]} with attractant concentration inside patches being 3 to 6 orders of magnitude higher than outside [2]}. This has led to a number of marine-specific evolutionary adaptations such as higher running speed in Pseudomonas haloplanktis [3]} and run-and-reverse (as opposed to run-and-tumble) chemotaxis in over 70% of marine bacterial species [4]}. Unfortunately, most experimental and theoretical studies to date consider chemotaxis in response to step functions or simple gradients [5]}, providing limited insights to how chemotaxis would function in different types of environments. In particular, there have few studies [6]}, [7]} analyzing chemotactic strategies in stochastic environments, which are likely to be the most important environment during the evolution of a chemotactic response.
